In more practical terms, blocking practice means asking a group of questions about a specific topic from class before moving on to questions about another topic in class. So, if I blocked my questions on the material covered in my class yesterday, I would first pose questions about Gestalt principles of perception (A) before asking about binocular and monocular depth cues (B) and then finish up with questions about schemas, assimilation, and accommodation (C). This is a very popular method for reviewing topics in class, on homework, or via some form of study guide. I use it often in my classes.
Interleaving practice says to split those topics up and ask a question or two about one topic before questioning about another topic and maybe another. Then return to the original concept and ask about it again before moving on to the other material again. While this may seem a little counterintuitive and will probably be a bit more cognitively challenging for students, there is evidence that it produces better learning outcomes long-term.
In the current study, 155 9th-12th grade students were given end of week practice quizzes for 4 weeks. Concepts would be assigned to a practice or non-practice condition. The information in the non-practice condition would not appear on any end of week quiz and only appeared on the final test one month after the final quiz. The information assigned to the practice condition would either be quizzed via blocked or interleaved questioning. This would alternate from week to week, meaning students would take two end of week quizzes that utilized blocked questioning and two that would utilize interleaved questioning.
One month after the final quiz, students were given a final test composed of questions from the blocked quizzes, questions from the interleaved quizzes, and questions from material assigned to the non-practice condition.