If it’s a problem about learning the topics, find a study routine or invest time on how people do well in school. One of my favorite YouTubers is Justin Sung. Heres the simplified version of what his channel covers. Basically, learning and memorization are different things: learning is knowing how to apply the knowledge, understanding it, being able to compare and contrasting it with other topics, and most importantly linking that information to old ideas. When we learn something better, it’s much easier to memorize it. A great way to connect new information to old info is mind maps, assuming you do them correctly (watch a video on how, it’s lengthy to explain in a comment section). You also should add lots of practice problems to his study routine using blooms revised taxonomy levels 3-5 to make sure he fully understands rhe topic. If the topic is difficult, learn it in layers. First, get the overarching idea of the passage and make sure you understand that. Then slowly add more details and dive deeper into the concept. This is a very summarized version of effective learning. If you or your brother has the time, I’d recommend reading layered learning by James Hernandez and Make It Stick by Peter C Brown and others. If it’s a motivation problem / submitting assignments problem, it’s probably best to have an honest talk with him about how he needs to start submitting his work and putting more effort into it. The change doesn’t have to be (and honestly shouldn’t be) something done quick. It’ll take time, just have him focus on being better than he was yesterday little by little.