I think SL primary is still a good school, though my kid is not studying there. (I have some friends' sons studying there). In terms of academic, SL uses English to teach Arithmetic and Common Knowledge, so their english level is much higher compared with those government subsid primarys.
however if u intend your boy to enter to their secondary school, (from my opinion), if your boy could achieve middle academic performance in the school, it is not difficult to go to their secondary. so better save around $4000 per month.
School fees + School Bus fees + lunch = almost $4000 (not include extra-cirriculum activities, eg piano, tution fees), my friend told me she has to spend around $5000+ each month for his son.