How is a mwalimu mkuu different from a mkuu wa shule and a kiranja?
'mwalimu mkuu' and 'mkuu wa shule' are more or less the same. 'Kiranja' is a class prefect/monitor
So the first two are basically like "principal" and the third is a student in the class?
yup. It's more common to use 'headmaster/headmistress', especially for heads of primary schools (yay colonization)
what does head teacher mean?