The following links are for pupils who are requiring extension materials either in class, or at home.
UKMT Challenges
The UKMT provides enriching problem solving challenges for pupils of all ages to develop their mathematical thinking and help them apply the skills and knowledge they have learned. The following link has a variety of old papers and solutions for pupils to try. In S1, they should concentrate on the first half of each paper but can attempt all of it.
NRICH
NRICH was set up by the University of Cambridge to develop pupils mathematical thinking. For the short problems, challenge level ☆ or ☆☆ would be advised.