Hi Vitth, thanks for contacting.
The whole idea behind the app is to offer you with the tools to keep track of your information and not to force anyone to do it in a very specific way. Every grade book is defined in different ways and despite being an app it should allow some 'personalization'.
The text+icons option is set by default because it offers more flexibility than the rest, but the icons meaning is something you decide. The usual,more useful icons are set first , + , - , check , and so on. And the unusual icons are supposed to be last.
I always missed being able to put an icon in a cell, so we did this one. After implementing, we thought... maybe two icons would be better... and then... lets put 4 in case someone needs it.
Concluding ... you'll probably only use one of the first icons (if any at all) , to check attendance, or to value positively (+,-) a student's action. Or maybe set the mail,phone or notepad icon to remember that you'll be contacting,calling, notifying the student's parents but it's up to you!