Study design for best teaching methods - how to avoid overly specific results?
No study in only a single class will be able to definitively answer such a question. The answer can only come from either a very large study or an accumulation of results over several small similar studies. 

If it is an attempt to get at the truth it will tell you very little. If it is an attempt to learn/teach something about experimentation it can have value. 

In the US, you would need to run this by your IRB. I don't know if Canada has similar regulations. But you are treating two parts of a class (human beings) differently and need to assure that neither group is disadvantaged in any way. It is unethical to do certain things when you strongly suspect that they are not effective, though I don't think that is a particular issue given your description. 

On the other hand, there is already a lot of research on learning that addresses just this question. If you haven't already explored it, you really should.