Someone upthread mentioned a programme on the Radio a couple of weeks ago - Inside Health, I think.
The medical person they had on said that readings of temperature can vary depending on what sort of thermometer you have, even, so going strictly by what the thermometer says doesn't actually tell you much about how healthy the child is, especially when they are in that "a little bit too warm" category.
She said the best thing to do was to use your instinct as to how the child actually was. So, if your child appears a bit warm but is otherwise fine, has energy, is eating etc, then they are fine. A slight rise in temp is in itself not a problem or an illness, or an indication of something serious about to happen. Kids have fluctuations in temperature.
A child can however be really poorly without even developing a temp. Her point was partly that it is important not to rely on temperature as the be-all-and-end-all to tell you if your child is ill or not - it may not rise and you may miss something as serious as meningitis if you are using temperature as your defining feature of illness. A child who is listless, won't eat, complains of headaches or similar is more likely to be genuinely ill than a kid who is half a degree above normal.
From what I can see, the OP started out seeming to say that her dd had been kept off with a temperature (37-39), and no other symptoms were mentioned initially. I think this is why the majority of people are saying the child should be in school - 37 is well within normal so I don't even count it as a temperature. If this really is the only problem and there are no other symptoms on this occasion then I'd agree with the dose of calpol and send her in. There's a big difference between 37 and 39 though, and I'd expect to see other problems arising as it got to or above 39 (certainly my dd gets weepy, sleeps almost constantly, won't eat and often refuses to drink by the time her temp hits that high). If she's got or has only just finished d&v, if there are other things than just a small temp going on (listless, won't eat etc) then keep her home regardless of whether her temp is 'normal' or not. But a small rise in temp on it's own isn't really a need to worry.
The level of absence I would say is worrying. What it is difficult to work out is how often the absences are occuring a) due to problems like d&v, or genuine fevers where the child is properly ill, in which case they are unavoidable or b) how often they are occurring because the child's temp is a 'bit high' even if no other symptoms are present. If it's more often the latter, then the low attendance is avoidable. It's not going to be unavoidable every time, but the attendance can be improved if you don't add to the necessary absences with unecessary ones (which I would say are the ones just due to a slight temp with no other symptoms present).
Sorry this is long but I was trying to be as clear as possible.