diff --git a/fnl/conjure/school.fnl b/fnl/conjure/school.fnl
index dd045ae9..8d3b5f23 100644
--- a/fnl/conjure/school.fnl
+++ b/fnl/conjure/school.fnl
@@ -12,11 +12,15 @@
   (buffer.upsert-hidden buf-name))
 
 (defn- append [lines]
-  (let [buf (upsert-buf)]
-    (nvim.buf_set_lines
-      buf
-      (if (buffer.empty? buf) 0 -1)
-      -1 false lines)))
+  (let [buf (upsert-buf)
+        current-buf-str (str.join "\n" (nvim.buf_get_lines 0 0 -1 true))
+        to-insert-str (str.join "\n" lines)]
+    (when (not (string.find current-buf-str to-insert-str 0 true))
+      (nvim.buf_set_lines
+        buf
+        (if (buffer.empty? buf) 0 -1)
+        -1 false lines)
+      true)))
 
 (defn- map-str [m]
   (.. (config.get-in [:mapping :prefix])
@@ -25,6 +29,11 @@
 (defn- progress [n]
   (.. "Lesson ["n "/7] complete!"))
 
+(defn- append-or-warn [current-progress lines]
+  (if (append lines)
+    (progress current-progress)
+    "You've already completed this lesson! You can (u)ndo and run it again though if you'd like."))
+
 (defn start []
   (when (not (editor.has-filetype? :fennel))
     (nvim.echo
@@ -68,7 +77,8 @@
         ["(school.lesson-1)"]))))
 
 (defn lesson-1 []
-  (append
+  (append-or-warn
+    1
     [""
      ";; Good job!"
      ";; You'll notice the heads up display (HUD) appeared showing the result of the evaluation."
@@ -92,23 +102,23 @@
      ";; Next, we have a form inside a comment. We want to evaluate that inner form, not the comment."
      (.. ";; Place your cursor on the inner form (the one inside the comment) and use " (map-str :eval_current_form) " to evaluate it.")
      "(comment"
-     "  (school.lesson-2))"])
-  (progress 1))
+        "  (school.lesson-2))"]))
 
 (defn lesson-2 []
-  (append
+  (append-or-warn
+    2
     [""
      ";; Awesome! You evaluated the inner form under your cursor."
      (.. ";; If we want to evaluate the outermost form under our cursor, we can use " (map-str :eval_root_form) " instead.")
      ";; Try that below to print some output and advance to the next lesson."
      ";; You can place your cursor anywhere inside the (do ...) form or it's children."
      "(do"
-     "  (print \"Hello, World!\")"
-     "  (school.lesson-3))"])
-  (progress 2))
+        "  (print \"Hello, World!\")"
+        "  (school.lesson-3))"]))
 
 (defn lesson-3 []
-  (append
+  (append-or-warn
+    3
     [""
      ";; You evaluated the outermost form! Nice!"
      ";; Notice that the print output was captured and displayed in the log too."
@@ -116,25 +126,25 @@
      (.. ";; Try pressing \"" (config.get-in [:eval :result_register]) "p to paste the contents of the register into your buffer.")
      (.. ";; We can also evaluate a form and replace it with the result of the evaluation with " (map-str :eval_replace_form))
      (.. ";; We'll try that in the next lesson, place your cursor inside the form below and press " (map-str :eval_replace_form))
-     "(school.lesson-4)"])
-  (progress 3))
+     "(school.lesson-4)"]))
 
 (defn lesson-4 []
-  (append
+  (append-or-warn
+    4
     [""
      ";; Well done! Notice how the resulting string in the log also replaced the form in the buffer!"
      ";; Next let's try evaluating a form at a mark."
      ";; Place your cursor on the next lesson form below and use mf to set the f mark at that location."
      (.. ";; Now move your cursor elsewhere in the buffer and use " (map-str :eval_marked_form) "f to evaluate it.")
      ";; If you use a capital letter like mF you can even open a different file and evaluate that marked form without changing buffers!"
-     "(school.lesson-5)"])
-  (progress 4))
+     "(school.lesson-5)"]))
 
 (def lesson-5-message
   "This is the contents of school.lesson-5-message!")
 
 (defn lesson-5 []
-  (append
+  (append-or-warn
+    5
     [""
      ";; Excellent!"
      ";; This is extremely useful when you want to evaluate a specific form repeatedly as you change code elsewhere in the file or project."
@@ -145,14 +155,14 @@
      ""
      (.. ";; You can evaluate visual selections with " (map-str :eval_visual))
      ";; Try evaluating the form below using a visual selection."
-     "(school.lesson-6)"])
-  (progress 5))
+     "(school.lesson-6)"]))
 
 (def lesson-6-message
   "This is the contents of school.lesson-6-message!")
 
 (defn lesson-6 []
-  (append
+  (append-or-warn
+    6
     [""
      ";; Wonderful!"
      ";; Visual evaluation is great for specific sections of a form."
@@ -161,16 +171,15 @@
      "school.lesson-6-message"
      ""
      (.. ";; Use " (map-str :eval_motion) "a( to evaluate the lesson form.")
-     "(school.lesson-7)"])
-  (progress 6))
+         "(school.lesson-7)"]))
 
 (defn lesson-7 []
-  (append
+  (append-or-warn
+    7
     [""
      ";; Excellent job, you made it to the end!"
      ";; To learn more about configuring Conjure, install the plugin and check out :help conjure"
      ";; You can learn about specific languages with :help conjure-client- and then tab completion."
      ";; For example, conjure-client-fennel-aniseed or conjure-client-clojure-nrepl."
      ""
-     ";; I hope you have a wonderful time in Conjure!"])
-  (progress 7))
+     ";; I hope you have a wonderful time in Conjure!"]))
diff --git a/lua/conjure/school.lua b/lua/conjure/school.lua
index fb106e2e..c90f0ab5 100644
--- a/lua/conjure/school.lua
+++ b/lua/conjure/school.lua
@@ -26,13 +26,20 @@ end
 _2amodule_locals_2a["upsert-buf"] = upsert_buf
 local function append(lines)
   local buf = upsert_buf()
-  local _1_
-  if buffer["empty?"](buf) then
-    _1_ = 0
+  local current_buf_str = str.join("\n", nvim.buf_get_lines(0, 0, -1, true))
+  local to_insert_str = str.join("\n", lines)
+  if not string.find(current_buf_str, to_insert_str, 0, true) then
+    local _1_
+    if buffer["empty?"](buf) then
+      _1_ = 0
+    else
+      _1_ = -1
+    end
+    nvim.buf_set_lines(buf, _1_, -1, false, lines)
+    return true
   else
-    _1_ = -1
+    return nil
   end
-  return nvim.buf_set_lines(buf, _1_, -1, false, lines)
 end
 _2amodule_locals_2a["append"] = append
 local function map_str(m)
@@ -43,6 +50,14 @@ local function progress(n)
   return ("Lesson [" .. n .. "/7] complete!")
 end
 _2amodule_locals_2a["progress"] = progress
+local function append_or_warn(current_progress, lines)
+  if append(lines) then
+    return progress(current_progress)
+  else
+    return "You've already completed this lesson! You can (u)ndo and run it again though if you'd like."
+  end
+end
+_2amodule_locals_2a["append-or-warn"] = append_or_warn
 local function start()
   if not editor["has-filetype?"]("fennel") then
     nvim.echo("Warning: No Fennel filetype found, falling back to Clojure syntax.", "Install https://github.com/Olical/aniseed for better Fennel support.")
@@ -56,58 +71,51 @@ local function start()
   local buf = upsert_buf()
   nvim.ex.edit(buf_name)
   nvim.buf_set_lines(buf, 0, -1, false, {})
-  local _4_
+  local _6_
   if ("<localleader>" == config["get-in"]({"mapping", "prefix"})) then
     if a["empty?"](nvim.g.maplocalleader) then
       nvim.g.maplocalleader = ","
       nvim.ex.edit()
-      _4_ = {";; Your <localleader> wasn't configured so I've defaulted it to comma (,) for now.", ";; See :help localleader for more information. (let maplocalleader=\",\")"}
+      _6_ = {";; Your <localleader> wasn't configured so I've defaulted it to comma (,) for now.", ";; See :help localleader for more information. (let maplocalleader=\",\")"}
     else
-      _4_ = {(";; Your <localleader> is currently mapped to \"" .. nvim.g.maplocalleader .. "\"")}
+      _6_ = {(";; Your <localleader> is currently mapped to \"" .. nvim.g.maplocalleader .. "\"")}
     end
   else
-    _4_ = nil
+    _6_ = nil
   end
-  return append(a.concat({"(module user.conjure-school", "  {require {school conjure.school}})", "", ";; Welcome to Conjure school!", ";; Grab yourself a nice beverage and let's get evaluating. I hope you enjoy!", "", ";; This language is Fennel, it's quite similar to Clojure.", ";; Conjure is written in Fennel, it's compiled to Lua and executed inside Neovim itself.", ";; This means we can work with a Lisp without installing or running anything else.", "", ";; Note: Some colorschemes will make the HUD unreadable, see here for more: https://git.io/JJ1Hl", "", ";; Let's learn how to evaluate it using Conjure's assortment of mappings.", ";; You can learn how to change these mappings with :help conjure-mappings", "", (";; Let's begin by evaluating the whole buffer using " .. map_str("eval_buf"))}, _4_, {"(school.lesson-1)"}))
+  return append(a.concat({"(module user.conjure-school", "  {require {school conjure.school}})", "", ";; Welcome to Conjure school!", ";; Grab yourself a nice beverage and let's get evaluating. I hope you enjoy!", "", ";; This language is Fennel, it's quite similar to Clojure.", ";; Conjure is written in Fennel, it's compiled to Lua and executed inside Neovim itself.", ";; This means we can work with a Lisp without installing or running anything else.", "", ";; Note: Some colorschemes will make the HUD unreadable, see here for more: https://git.io/JJ1Hl", "", ";; Let's learn how to evaluate it using Conjure's assortment of mappings.", ";; You can learn how to change these mappings with :help conjure-mappings", "", (";; Let's begin by evaluating the whole buffer using " .. map_str("eval_buf"))}, _6_, {"(school.lesson-1)"}))
 end
 _2amodule_2a["start"] = start
 local function lesson_1()
-  append({"", ";; Good job!", ";; You'll notice the heads up display (HUD) appeared showing the result of the evaluation.", ";; All results are appended to a log buffer. If that log is not open, the HUD will appear.", ";; The HUD closes automatically when you move your cursor.", "", ";; You can open the log buffer in a few ways:", (";;  * Horizontally - " .. map_str("log_split")), (";;  * Vertically - " .. map_str("log_vsplit")), (";;  * New tab - " .. map_str("log_tab")), "", (";; All visible log windows (including the HUD) can be closed with " .. map_str("log_close_visible")), ";; Try opening and closing the log window to get the hang of those key mappings.", ";; It's a regular window and buffer, so you can edit and close it however you want.", ";; Feel free to leave the log open in a split for the next lesson to see how it behaves.", "", ";; If you ever need to clear your log you can use the reset mappings:", (";; * Soft reset (leaves windows open) - " .. map_str("log_reset_soft")), (";; * Hard reset (closes windows, deletes the buffer) - " .. map_str("log_reset_hard")), "", ";; Next, we have a form inside a comment. We want to evaluate that inner form, not the comment.", (";; Place your cursor on the inner form (the one inside the comment) and use " .. map_str("eval_current_form") .. " to evaluate it."), "(comment", "  (school.lesson-2))"})
-  return progress(1)
+  return append_or_warn(1, {"", ";; Good job!", ";; You'll notice the heads up display (HUD) appeared showing the result of the evaluation.", ";; All results are appended to a log buffer. If that log is not open, the HUD will appear.", ";; The HUD closes automatically when you move your cursor.", "", ";; You can open the log buffer in a few ways:", (";;  * Horizontally - " .. map_str("log_split")), (";;  * Vertically - " .. map_str("log_vsplit")), (";;  * New tab - " .. map_str("log_tab")), "", (";; All visible log windows (including the HUD) can be closed with " .. map_str("log_close_visible")), ";; Try opening and closing the log window to get the hang of those key mappings.", ";; It's a regular window and buffer, so you can edit and close it however you want.", ";; Feel free to leave the log open in a split for the next lesson to see how it behaves.", "", ";; If you ever need to clear your log you can use the reset mappings:", (";; * Soft reset (leaves windows open) - " .. map_str("log_reset_soft")), (";; * Hard reset (closes windows, deletes the buffer) - " .. map_str("log_reset_hard")), "", ";; Next, we have a form inside a comment. We want to evaluate that inner form, not the comment.", (";; Place your cursor on the inner form (the one inside the comment) and use " .. map_str("eval_current_form") .. " to evaluate it."), "(comment", "  (school.lesson-2))"})
 end
 _2amodule_2a["lesson-1"] = lesson_1
 local function lesson_2()
-  append({"", ";; Awesome! You evaluated the inner form under your cursor.", (";; If we want to evaluate the outermost form under our cursor, we can use " .. map_str("eval_root_form") .. " instead."), ";; Try that below to print some output and advance to the next lesson.", ";; You can place your cursor anywhere inside the (do ...) form or it's children.", "(do", "  (print \"Hello, World!\")", "  (school.lesson-3))"})
-  return progress(2)
+  return append_or_warn(2, {"", ";; Awesome! You evaluated the inner form under your cursor.", (";; If we want to evaluate the outermost form under our cursor, we can use " .. map_str("eval_root_form") .. " instead."), ";; Try that below to print some output and advance to the next lesson.", ";; You can place your cursor anywhere inside the (do ...) form or it's children.", "(do", "  (print \"Hello, World!\")", "  (school.lesson-3))"})
 end
 _2amodule_2a["lesson-2"] = lesson_2
 local function lesson_3()
-  append({"", ";; You evaluated the outermost form! Nice!", ";; Notice that the print output was captured and displayed in the log too.", ";; The result of every evaluation is stored in a Neovim register as well as the log.", (";; Try pressing \"" .. config["get-in"]({"eval", "result_register"}) .. "p to paste the contents of the register into your buffer."), (";; We can also evaluate a form and replace it with the result of the evaluation with " .. map_str("eval_replace_form")), (";; We'll try that in the next lesson, place your cursor inside the form below and press " .. map_str("eval_replace_form")), "(school.lesson-4)"})
-  return progress(3)
+  return append_or_warn(3, {"", ";; You evaluated the outermost form! Nice!", ";; Notice that the print output was captured and displayed in the log too.", ";; The result of every evaluation is stored in a Neovim register as well as the log.", (";; Try pressing \"" .. config["get-in"]({"eval", "result_register"}) .. "p to paste the contents of the register into your buffer."), (";; We can also evaluate a form and replace it with the result of the evaluation with " .. map_str("eval_replace_form")), (";; We'll try that in the next lesson, place your cursor inside the form below and press " .. map_str("eval_replace_form")), "(school.lesson-4)"})
 end
 _2amodule_2a["lesson-3"] = lesson_3
 local function lesson_4()
-  append({"", ";; Well done! Notice how the resulting string in the log also replaced the form in the buffer!", ";; Next let's try evaluating a form at a mark.", ";; Place your cursor on the next lesson form below and use mf to set the f mark at that location.", (";; Now move your cursor elsewhere in the buffer and use " .. map_str("eval_marked_form") .. "f to evaluate it."), ";; If you use a capital letter like mF you can even open a different file and evaluate that marked form without changing buffers!", "(school.lesson-5)"})
-  return progress(4)
+  return append_or_warn(4, {"", ";; Well done! Notice how the resulting string in the log also replaced the form in the buffer!", ";; Next let's try evaluating a form at a mark.", ";; Place your cursor on the next lesson form below and use mf to set the f mark at that location.", (";; Now move your cursor elsewhere in the buffer and use " .. map_str("eval_marked_form") .. "f to evaluate it."), ";; If you use a capital letter like mF you can even open a different file and evaluate that marked form without changing buffers!", "(school.lesson-5)"})
 end
 _2amodule_2a["lesson-4"] = lesson_4
 local lesson_5_message = "This is the contents of school.lesson-5-message!"
 _2amodule_2a["lesson-5-message"] = lesson_5_message
 local function lesson_5()
-  append({"", ";; Excellent!", ";; This is extremely useful when you want to evaluate a specific form repeatedly as you change code elsewhere in the file or project.", (";; Try inspecting the contents of the variable below by placing your cursor on it and pressing " .. map_str("eval_word")), "school.lesson-5-message", "", ";; You should see the contents in the HUD or log.", "", (";; You can evaluate visual selections with " .. map_str("eval_visual")), ";; Try evaluating the form below using a visual selection.", "(school.lesson-6)"})
-  return progress(5)
+  return append_or_warn(5, {"", ";; Excellent!", ";; This is extremely useful when you want to evaluate a specific form repeatedly as you change code elsewhere in the file or project.", (";; Try inspecting the contents of the variable below by placing your cursor on it and pressing " .. map_str("eval_word")), "school.lesson-5-message", "", ";; You should see the contents in the HUD or log.", "", (";; You can evaluate visual selections with " .. map_str("eval_visual")), ";; Try evaluating the form below using a visual selection.", "(school.lesson-6)"})
 end
 _2amodule_2a["lesson-5"] = lesson_5
 local lesson_6_message = "This is the contents of school.lesson-6-message!"
 _2amodule_2a["lesson-6-message"] = lesson_6_message
 local function lesson_6()
-  append({"", ";; Wonderful!", ";; Visual evaluation is great for specific sections of a form.", (";; You can also evaluate a given motion with " .. map_str("eval_motion")), (";; Try " .. map_str("eval_motion") .. "iw below to evaluate the word."), "school.lesson-6-message", "", (";; Use " .. map_str("eval_motion") .. "a( to evaluate the lesson form."), "(school.lesson-7)"})
-  return progress(6)
+  return append_or_warn(6, {"", ";; Wonderful!", ";; Visual evaluation is great for specific sections of a form.", (";; You can also evaluate a given motion with " .. map_str("eval_motion")), (";; Try " .. map_str("eval_motion") .. "iw below to evaluate the word."), "school.lesson-6-message", "", (";; Use " .. map_str("eval_motion") .. "a( to evaluate the lesson form."), "(school.lesson-7)"})
 end
 _2amodule_2a["lesson-6"] = lesson_6
 local function lesson_7()
-  append({"", ";; Excellent job, you made it to the end!", ";; To learn more about configuring Conjure, install the plugin and check out :help conjure", ";; You can learn about specific languages with :help conjure-client- and then tab completion.", ";; For example, conjure-client-fennel-aniseed or conjure-client-clojure-nrepl.", "", ";; I hope you have a wonderful time in Conjure!"})
-  return progress(7)
+  return append_or_warn(7, {"", ";; Excellent job, you made it to the end!", ";; To learn more about configuring Conjure, install the plugin and check out :help conjure", ";; You can learn about specific languages with :help conjure-client- and then tab completion.", ";; For example, conjure-client-fennel-aniseed or conjure-client-clojure-nrepl.", "", ";; I hope you have a wonderful time in Conjure!"})
 end
 _2amodule_2a["lesson-7"] = lesson_7
 return _2amodule_2a
\ No newline at end of file