... Those sample questions don't seem so scary. Would there be any harm in him trying the samples. That would make me feel more relaxed. Does any body think it would be realistic to say if he can do those samples he will be fine. I think it's ok if he can't do some of the questions.
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As I said in my post above -- Have him do the sample questions! That's what they are for, to let the kids know what to expect. I do think the sample questions are more like some of the easier ones they'll get on the test.
It wouldn't hurt to give a quick course on fractions and decimals, he may not have done that in the third grade at school. But it will help to know that on the math portion of the test.