My opinion is DON'T rely on dream signs. if you don't dream about school then no lucidity. You need to do something more than just waiting for a dream about school. If you are going to try to get lucid via DILD then you MUST practice being aware. You probably can't be aware 24/7 so simply do it in small doses. When doing a reality check REALLY question your surroundings. Take a good look at everything. Then check your memory and explain to yourself what you are doing, why you are doing it, and what were you doing earlier. By doing this you will eventually become independent of dream signs and will become aware in your dreams in many other settings besides school. Hope this helps!