I learned from another teacher that the use of mini quizzes can really help students with material they consider difficult, as in math for example. During a four hour class, the students may take four tiny quizzes--one at the end of each hour--which each consist of four or five questions on the skill we just covered. The quizzes are graded right there over the break, and both the student and I get a good idea of where they stand right there.
