Hi Embrace
I highly recommend children to finish their abacus class before they start pri 1 as I heard from my friends that many children feel confused with the different methodology taught in primary schools vs their abacus/mental arithmatic class.
My girl, currently in K2, had recently completed her Mental Arithmatic (MA) course at E&P learning place, well before she starts Pri 1 next year. She started her course in Feb 2011 with abacus (3 workbooks plus grading test), followed by Mental Arithmatic (8 workbooks plus grading tests) starting mid 2011.
I've told her many times to follow what was taught in her K2 Childcare and only use her MA to double-check her answers. Generally, I find the MA class v good as it has enhanced my child's focus, help her to do her sums in great speed and sensitive with numbers. In fact, she enjoyed her MA so much that she did her workbook daily. And I'm glad that I won't have to worry about her addition, subtraction, multiplication and division since she's capable of dealing with figures running into hundred thousands with 2 decimal places.