The website of the wonderful Anne Watson and John Mason.
PM Theta
Dr Frost Maths
Free online resources for KS3 to KS5. Videos, worksheets, lessons etc.
Diagnostic Questions
This is a very clever bank of resources with thousands of student answers, revealing the most common misconceptions in primary and secondary maths. Sign up for free.
Maths Week London
A new initiative to get London fired up about all things maths.
Maths Frame
Lots of great maths games and tools, written by former primary teacher Ted Burch, including the old Interactive Teaching programmes, reprogrammed to work on any platform.
Mathsbot
A stunning and free range of resources produced by maths teacher Jonathan Hall. Suitable for both primary and secondary.
TES Maths Community
Source of interesting debate and discussion between teachers. Tends to be mostly secondary but some primary issues are discussed too.
NRICH
This website is from a Cambridge-based organisation, specialising in rich tasks for both primary and secondary school children. An excellent source of problem-solving tasks with notes for teachers.
Resourcaholic
Secondary maths teacher Jo Morgan has spent years curating the ‘best of the web’ in terms of secondary school maths teaching resources. Check out her ever-growing and entirely free collection here.