It's important to understand not every child learns at the same rate and some have a better grasp at certain subjects than others. And one of the more difficult subject areas are the sciences.

Repetition and flash cards have been the most effective method in my experience, with myself and peers using them to quiz themselves and build a strong foundation for each subject areas.

The first thing to do with any student is get an understanding of their proficiency and take notes around what they think is their issues are. Beginning with their current level of understanding I can begin to slowly advance their knowledge with mock questions, walking them through solutions and the framework on how to answer them.

Questions by the pupil should not be dismissed as it's important they are comfortable listening to you as well as knowing they will be to. I also understand that I may go too fast for students, so I won't be insulted or annoyed if I am told to slow down or repeat sections.

Giving a few questions or a worksheet that a student can take from a session and attempt in their own time in a comfortable environment is key. Because no matter how well explained a subject or lesson is, it means nothing if the pupil cannot recall the information when they need to. It will not be pages of work, just 2-3 questions that over the topics from the session. And if repeated enough times, a student will get faster and more effective at solving problems and even learning further topics faster.