@mbhunia
You will get arrear from that school where your pay was fixed. If fixation was done in old school and you are now in new school because of mutual transfer you will get all the arrear from old school.
Pay of my wife (AT) was fixed in old school. She got 1st installment while in service in old school. After that she joined a new school again through SSC in Oct.,2009. After joining the new school in Oct.,2009 she also got 2nd & 3rd installments from old school.