As a (UK, math(s)) teacher I have to warn you that gaming the scores will inevitably happen when you have scores and those scores may impact on career.

http://www.ofsted.gov.uk/resources/mathematics-made-measure

Long, UK specific, but possibly of interest to those with school age children in educational systems using these metrics.

PS: most of the data I plot on scatter plots has low density and high variability so little stacking.