My son is currently doing iGCSE physics course (they also have biology, chemistry and dual science, plus A levels). Once you have paid you gain access to the site and the whole course. You can work through at your own pace. My son is doing one module each week which generally consists of a teaching video between 20 – 45mins, sometimes a few extra YouTube videos which are short), an online assessment (on average about 15 questions) and sometimes an assignment to print out which has exam style questions.  Every so often there is a mock exam paper which has about 4 questions on and laid out exactly the same as an exam question would be. The mock exams and print out assignments all come with answer sheets. Once a week there is an option to log in to a live Facebook session where the course leader takes questions and work through problems with the students. 

Once you have got your head around the set up, which I confess took me a little time (although the SWSS were amazing in helping me set up), it is fantastic. My son is finding the teaching videos engaging, he is definitely challenged by the course but we did start this september when he was 13 (so in theory he should have started next year). However, he has stayed on target and reviewing the sessions he has already done this year at present and really seeing he has learnt a lot. 

The SWSS are great at responding to questions and have been very supportive for us on our journey. My understanding is that we have to organise the exam centre and pay for the exam when we reach that stage.