I have been working with my students on their writing for the past 5 months in an ESL lab at our college, and the most common mistake that I see on a daily basis is the misuse of "affect" and "effect." However, students learning English are not the only ones that make this mistake. Many native speakers of English don't know the difference between the two words and I myself have used them incorrectly. Today, I was editing my graduate thesis paper on teacher and student perceptions of music to support second language acquisition and I found that I made a mistake with "affect" and "effect."
My sentence read, "In this study, the data suggests that the top down approach is more effective than responding to student needs by using a bottom down approach." However, it should read "in this study, the data suggests that the top down approach is more affective than responding to student needs by using a bottom down approach."
This is because in the sentence I am using affective as a noun, not effective as a verb. Just remember,
Sleeping late affects his ability to do good on his tests. The sleeping pills had a good effect on him because he slept 8 hours that night.