hard to know for certain if it's the best decision
Because the decision you are considering is essentially a "whole grade acceleration", you may wish to look at the Iowa Acceleration Scale (
IAS) as an objective measure. Possibly the school is already aware of this tool and is using it?
Because gifted children may grow academically/intellectually by leaps and bounds, then experience a plateau, or show marked asynchrony, parents may find themselves frequently re-evaluating the "fit" of the learning environment and making fresh decisions about the best placement option (or least-worst fit) each year. Taking it a year at a time and knowing adjustments can be made as your child's needs change, can help increase confidence in decisions.
The
IAS-3 manual shares these research results on page 122:
In one study, it was determined that when students were selected for early entrance to school based on indicators of readiness, rather than chronological age, their performance and adjustment to school was equal to or surpassed that of students who were placed in kindergarten based on their chronological age (Gagne & Gagnier, 2004).
