Note that you can apply filters, so you could choose to look at a more limited age range such as 11-14.

To highlight some of these resources (images link to the STEM learning resource:

By David Kirby and Peter Patilla we have Maths Investigationsand accompanying comprehensive teachers’ guide which contains 80 cards based on 10 themes.

David Kirby and Peter Patilla – Maths Investigations

There are many textbooks available which were published some years ago but are still very useful and in fact include chapters on topics new to GCSE such as Venn Diagrams and sets.

A Nelson Thornes series for GCSE Maths is available which was developed for the days of the three tier GCSE Mathematics. These are attractive in their presentation and could be useful for projecting examples.