diff --git a/src/jupyter_contrib_nbextensions/nbextensions/exercise/main.js b/src/jupyter_contrib_nbextensions/nbextensions/exercise/main.js
index d8050fbb6..91f8161ca 100644
--- a/src/jupyter_contrib_nbextensions/nbextensions/exercise/main.js
+++ b/src/jupyter_contrib_nbextensions/nbextensions/exercise/main.js
@@ -4,6 +4,7 @@
 // Hide or display solutions in a notebook
 
 /*
+December  6, 2017 @jcb91: use bootstrap 'hidden' class to play nicely with collapsible_headings
 December 30, 2015: update to 4.1
 Update december 22, 2015:
   Added the metadata solution_first to mark the beginning of an exercise. It is now possible to have several consecutive exercises. 
@@ -48,7 +49,7 @@ define([
             IPython.notebook.select_next();
             cell = IPython.notebook.get_selected_cell();
             while (cell_index++<ncells & cell.metadata.solution !=undefined & cell.metadata.solution_first !=true) {
-                cell.element.show();
+                cell.element.removeClass('hidden');
                 cell.metadata.solution = "shown";
                 IPython.notebook.select_next();
                 cell = IPython.notebook.get_selected_cell();
@@ -60,7 +61,7 @@ define([
             IPython.notebook.select_next();
             cell = IPython.notebook.get_selected_cell(); 
             while (cell_index++<ncells & cell.metadata.solution !=undefined & cell.metadata.solution_first !=true) {
-                cell.element.hide();
+                cell.element.addClass('hidden');
                 cell.metadata.solution = "hidden"
                 IPython.notebook.select_next();
                 cell = IPython.notebook.get_selected_cell();                
@@ -93,7 +94,7 @@ define([
             delete cell.metadata.solution_first;
             while (cell.metadata.solution != undefined & cell.metadata.solution_first !=true ) {
                 delete cell.metadata.solution;
-                cell.element.show();
+                cell.element.removeClass('hidden');
                 IPython.notebook.select_next();
                 cell = IPython.notebook.get_selected_cell()
             }
@@ -123,7 +124,7 @@ define([
                     cell = lcells[k];
                     //console.log("new cell:", icells[k]);
                     cell.element.css({"background-color": "#ffffff"});
-                    cell.element.hide();
+                    cell.element.addClass('hidden');
                     cell.metadata.solution = "hidden";
                 }
             }
@@ -183,12 +184,7 @@ function load_ipython_extension(){
     for(var i in cells){
         var cell = cells[i];
         if (found_solution == true && typeof cell.metadata.solution != "undefined" && cell.metadata.solution_first !=true) {
-            if (cell.metadata.solution  === "hidden") {
-                            cell.element.hide() 
-               }
-            else {
-                cell.element.show()
-            }
+            cell.element.toggleClass('hidden', cell.metadata.solution  === 'hidden');
         } else {
             found_solution = false
         }
diff --git a/src/jupyter_contrib_nbextensions/nbextensions/exercise2/main.js b/src/jupyter_contrib_nbextensions/nbextensions/exercise2/main.js
index cb3e9c37e..3a700c4c5 100644
--- a/src/jupyter_contrib_nbextensions/nbextensions/exercise2/main.js
+++ b/src/jupyter_contrib_nbextensions/nbextensions/exercise2/main.js
@@ -3,6 +3,7 @@
 
 // Hide or display solutions in a notebook
 
+// dec 6, 2017 @jcb91: use bootstrap 'hidden' class to play nicely with collapsible_headings
 // december 30, 2015: update to notebook 4.1.x
 // updated on december 22, 2015 to allow consecutive exercises
 // exercise2: built by @jfbercher from an earlier work by @junasch october 2015) - see readme.md
@@ -16,7 +17,7 @@
             IPython.notebook.select_next();       
             cell = IPython.notebook.get_selected_cell(); 
             while (cell_index++<ncells & cell.metadata.solution2 !=undefined & cell.metadata.solution2_first !=true) {
-                cell.element.show();
+                cell.element.removeClass('hidden');
                 cell.metadata.solution2 = "shown";
                 IPython.notebook.select_next();       
                 cell = IPython.notebook.get_selected_cell();         
@@ -31,7 +32,7 @@
             IPython.notebook.select_next();       
             cell = IPython.notebook.get_selected_cell(); 
             while (cell_index++<ncells & cell.metadata.solution2 !=undefined & cell.metadata.solution2_first !=true) {               
-                cell.element.hide();
+                cell.element.addClass('hidden');
                 cell.metadata.solution2 = "hidden";
                 IPython.notebook.select_next();       
                 cell = IPython.notebook.get_selected_cell();          
@@ -105,7 +106,7 @@ id=\"myCheck' + cbx + '\"  >\
             delete cell.metadata.solution2_first;
             while (cell.metadata.solution2 != undefined & cell.metadata.solution2_first !=true) {
                 delete cell.metadata.solution2;
-                cell.element.show();
+                cell.element.removeClass('hidden');
                 IPython.notebook.select_next();
                 cell = IPython.notebook.get_selected_cell()
             }
@@ -119,7 +120,7 @@ id=\"myCheck' + cbx + '\"  >\
                 for  (var k = 1; k < lcells.length; k++){
                     cell = lcells[k];
                     cell.element.css({"background-color": "#ffffff"});
-                    cell.element.hide();
+                    cell.element.addClass('hidden');
                     cell.metadata.solution2 = "hidden";
                 }
                 IPython.notebook.select(icells[0]);  //select first cell in the list
@@ -167,12 +168,7 @@ function load_ipython_extension(){
     for(var i in cells){
         var cell = cells[i];
         if (found_solution == true && typeof cell.metadata.solution2 != "undefined" && cell.metadata.solution2_first !=true) {
-            if (cell.metadata.solution2  === "hidden") {
-                        cell.element.hide();
-               }
-            else {
-                cell.element.show();
-            }
+            cell.element.toggleClass('hidden', cell.metadata.solution2  === 'hidden');
         } else {
             found_solution = false
         }