it took me a while because I used to rake, but you eventually get it. Your teacher can not expect you to learn alternation in a span of a week. It's impossible...it took me a few months.
If you want to learn alternation, do that. If you want to learn raking, do that. Many threads have tried to find which is superior, but the pros and cons go for and against each. So, there is no real perfect method. Just pick the one you like or learn to use both.
One of the best exercises that helps is this:
http://www.warwickbass.com/basssurvi...n_9fingers.htm Check exercise 4