You most certainly do not require even GCSEs to pass the JAR ATPL exams. In fact, as some people have learned to their cost, Knowing the true facts about some of these subjects can be a handicap. What you need to know is the JAR facts.
In the case of the technical subjects, a basic grounding in such things as newtons laws, trigonometry, and how to use a calculator is enough to start with. Your instructors will help you build on this. (Yes they will probably complain, but that's just normal). If that's not convinced you, then consider this. In one of the 4 week CAA courses at PPSC last year the electrics instructor was dealing with transformer theory. One of the students couldn't quite grasp how to work out the output for a given input and number of windings. The instructor said "just think of the ratios of primary windings to secondary windings". He was a bit exasperated when the student said "what's a ratio". The student then went on to pass everything first time.
You can pass the exams if you are prepared to work hard enough.