I don't have kids (I'm a teenager) so I can only go off of what my mom did for me. I've only been taken out for vacation (missing more than one day. One day before a break happened frequently) in 1st gade (missed 3 days), 3rd grade (2-4 days), and freshman year of hs (4 days). She was fine taking me out when I was younger and even freshman year but our next trip is scheduled for next year when I will be a junior which is obviously a very important year for me so our trips are VERY tailored to my break schedule. This may be easier for us since every teacher I've ever had has had no problems giving me hw or missed work and scheduling makeup tests, etc. and the school doesn't make up do anything extra (paperwork, etc.) that I have read that a lot of other people have to do to take their kids out. I'd base it on how well they're doing (which is great that it isn't a problem for ya) and how important that particular year is. Obviously every year is important but some [usually the higher ones (except if you ask my mother 'I'd rather you miss 3 months of your senior year than 4 days in your junior!')], as you know, are more important than others.