I had experiences of doing IELTS both BC and ACBT..Both in their Kandy branches...But, I didn't follow any classes..However, I went for a workshop conducted by ACBT just before the exam. It was a 3 day one and cost me around 8000 LKR. I must say it was a really good one..Even, BS was also not bad..I did IELTS exams there just for a change, and to increase my marks. ( to get 8 each for each of the modules)
I have referred mostly the online materials and the recommended Cambridge Books. And also used the booklet given by both BC and ACBT at the time of registration...When it comes to writing, you'll need to practice and it's better if you have someone to work with you. The person should NOT has to be a teacher, but a friend who has a good knowledge, and can correct your papers...And also, please be mindful on paragraphing, grammar, spellings etc. Sometimes, that will be the difference between 6.5 and 7.0..