For OCR’s teaching and learning resources see this page and also this for OCR(MEI).
I do like OCR’s check in tests for GCSE and we now have section Check In tests for A Level Specification A and a set for OCR Mathematics B (MEI).
You can read OCR’s Guide for the detail on the Check In tests each of which has 10 questions: Questions 1-4 are routine procedural questions and question 5-10 focus on the overarching themes: Mathematical argument, language and proof, Mathematical problem solving and Mathematical modelling. Questions marked with an asterisk are for students on the full two year A Level course.
The whole series of these excellent Section Check In Tests include fully worked solutions; each test includes routine procedural questions, problem solving questions and also an extension activity.
We also have Teaching Activities which include exercises using OCR’s large data set for OCR Mathematics A (H230/H240) for teaching Statistics.
Included with the Teacher Guides, notes on OCR’s large data set for OCR Mathematics A (H230/H240) are provided.
Note too the comprehensive set of Delivery Guides on planning and teaching the specification. These are available for both OCR’s specifications. Each Delivery Guide includes many further references to resources, with common content for all examination boards these are useful for everyone.
Looking at the Delivery Guide on Proof, I like this GeoGebra Alternate Segment Theorem Proof by Michael Borcherds.
Also we have a proof of Pythagoras, attributed by Americans to President James Garfield.
This could also be a rather nice starter for younger students.