You may be considering 12+ for a number of reasons:
Different Grammar Schools have different entry requirements, so it's important to check with the individual school beforehand, but generally 12+ consists of a CAT (Cognitive Abilities Test). In this test four types of reasoning are usually tested: verbal, non-verbal, spatial and quantative . Past papers aren't released and there is a limited amount of material out there.
However, through my experience with the 11+ and the use of puzzles and problem solving I have successfully prepared pupils for this largely unknown exam and currently have a 100% pass rate.
Moving to secondary school is a huge change in children's lives, particularly for those moving from small rural schools. Post 11+, many pupils stay on to make sure they are well prepared for SATs . After the exams in May, we make an early start on Year 7 Maths and English which gives children a much needed confidence boost for those first weeks in September and October. I often continue tuition well into Year 7, concentrating on areas they may be struggling with in class. Many find it difficult to admit they don't understand in a new classroom environment with unknown teachers and peers. I offer that all important continuation from primary school.