\input zb-basic \input zb-matheduc \iteman{ZMATH 2015f.00558} \itemau{Littler, Graham; Koman, Milan} \itemti{On zig-zag sums.} \itemso{Math. Teach. (Derby) 232, 9-12 (2013).} \itemab Summary: The tasks and activities rely on the ideas first introduced in Part 1 [the author; Math. Teach. (Derby) 231, 9--14 (2012; ME 2013d.00373)]. The authors continue to motivate with pattern. Learners are invited to enquire, to seek patterns, and to hypothesise. The context of simple number squares enables all students to engage with the tasks. These are undoubtedly ideas for the classroom, but prior experience of what happens will enrich both the classroom dialogue, and the learning opportunities. The authors seek to engage, motivate, and challenge students in a variety of ways that might lead to zig-zag sums becoming common classroom parlance. \itemrv{~} \itemcc{F30 D50 A20 D40} \itemut{number squares; addition squares; zig-zag squares; student activities; problem posing; changing tasks; generalization; pattern recognition; double zig-zag sums; zig-zag rectangles; rectangular arrays; visualisation; numerical operations in a non-standard situation; non-routine problems} \itemli{http://www.atm.org.uk/login.aspx?ReturnUrl=http%3a%2f%2fwww.atm.org.uk%2fMathematics-Teaching-Journal-Archive%2f3931} \end