Many of us are not aware that there is an aptitude tests on the last day of the UPSR. You can't "study" for this aptitude test because there are no reference materials available.
Relax. Don't worry about it. The paper is 1 1/2 hours long and include IQ tests and personality assessments. You won't find any books on it because there is none. There are no past year papers as well.
There is however, a teacher's blog which gives some examples of the UPSR Aptitude Test in case you are interested. You can take a look at it to have an idea but there is no need to get your child to "study" it. This will only stress them up further.
parents kids taking the UPSR 2015, the last batch to do so. GOOD LUCK AND STAY CALM!