Please find attached the solutions from three Year 8 students.
I apologise for the quality of some of the scanning but hopefully they will still be able to be followed.
The first page is Marjolaine Briscoe's solution.
The 2nd, 3rd, 7th and 8th pages are Misha Voloboev's solution (unfortunately he used colour to distinguish his solutions on each page but the writing provides some extra detail that Marjolaine's does not).
The 4th, 5th and 6th pages are Jacob Chevalier Drori's solution which is the least complete but again provides a nice way of thinking about the problem.
I hope this is OK to submit all three solutions to you (I got 23 and have chosen the most impressive!), in particular given that they are older than the suggested challenge age but getting all the possibles in a systematic way was certianly a good challenge for them!
Thanks,
Andy