I live in South Brooklyn, and all the moms around here rely on educational alternatives for their children. We all feel that the NYC school system is so poor, and the curriculum is well below where it should be, that almost everyone sends their child to extra classes, tutoring, or other mentally stimulating activities.
In South Brooklyn, the most popular alternative is an after-school center called Brainy Academy located in Sheepshead Bay. They offer Montessori classes in Brooklyn that are excellent for young children. Montessori classes improve a young child's cognition, language, social aptitude, and give them the building blocks for early math and reading. Most of the parents have found this program to be successful for their kids, and the kids love the area! Montessori classrooms are set up with special approved materials that are brightly colored and interactive. Brainy Academy is in a brand new location and all of their materials are new.
Other places like Fast Track Kids, also located in Sheepshead Bay are popular, but they have a strict set curriculum and you have to enter your child for a minimum of two years, whereas Brainy is set up with small classes and either one-on-one tutoring or tutoring in small groups, so parents can control the curriculum as they see fit.
Preparing children for kindergarten is vital. By kindergarten your children should be ready to read and write, and it does take a certain amount of development to get them there. Good luck!