I just got an A in chemistry at A level (Edexcel). I really struggled in both year 12 and year 13, getting Bs and Cs in all my class tests etc when I needed As. The best way I found to pull my grade up for end of year exams (instead of AS levels) and then the real thing was by doing past papers. I did TONS. However I found the best revision method was to do the paper then within the next week add it to my 'Bulletproof Booklet'. That is a word document containg a table with the column titles 'Past Pare' (so which one I'd just completed), 'Topic', 'Question', 'What I did wrong', 'Correct answer'. I filled in this table, adding rows as I went, for every single question I got wrong. 1 markers, multiple choice, 6 markers, diagrmas and equations. All of them. It highlighted the areas I was weakest, such as on particular types of questions I wouldn't use a particular key word or even wider areas I needed to go over the textbook again. Oh and before any tests a friend of a similar ability level and I woudl go through the topics we needed to know verbally. We skimmed through them and chatted about it so very informal but very quick so we got through a lot. Don't panic if you're not getting the grades you want in class, just persist with the work and every little bit of effort you put in, even 10 minutes thinking about the colours of flame tests, will help. Sorry I haven't put in any paragraphs, my enter key is broken!