Interesting, I also felt like this when I was at school (i'm 23 now though). ​ I would say the reason why you feel so confident in Maths class, is because you have probably asked a question before and it was well received, meaning you built a positive reinforcement in regards to asking questions in maths class in your brain. ​ So my advice would be, the next time you feel like asking a question in English class go for it! Don't worry if you stammer. Hopefully it goes well and then you will also feel confident in English class. ​ The most important thing to remember with stammering, is never let it take control. If you want to ask a question, override the worry in your brain and 'just do it'.