No, you are not. Because you are in the field, you know the difference. A child who is "behind" is one who is not at their level of achievement, but their ultimate level of achievement, given resources, is within the "normal" range.

A child who is "retarded," a term we no longer use, is recognized as intellectually different and, given appropriate resources, will rise to the highest level of their achievement, but their ultimate level of achievement is expected to be lower than the "normal range. This is not an issue when kids with those needs are identified appropriately. It is an issue when kids who have been denied access to education in one way or another are labeled "behind" in their capacities rather than their achievement, both actual and potential.