You'll need to describe your data model, the tables and relationships used. What you describe is possible but the devil is in the details you have not yet shared about your project.
The version of FileMaker that you are using is also important.
Summary reports, relationships, filtered portals and ExecuteSQL (if using version 12 or newer) could all be used to produce such a count. And this is also data that can be charted from either a found set or possibly a set of related records.
Sorry about the lack of info. Haven't worked with FMP or this forum for a while now and am a bit rusty. I am using FMP 13 Advanced and the field I am referring to is a simple calculation field that looks at another field (score) and subtracts 1 from that score. If the score is a negative number that means that the child is below expected level, a score of zero would mean the child is at expected level and a score 1 or above would mean that the child is above expected level. I want to use fusion charts to graph the number of students below, at or above expected level.
Hope that clears things up a bit.
But how are your tables set up?
Do you have a table of students with one record per student with one such calculation field returning that value?
If so, this is a pretty simple chart to set up. Define a "count of" summary field that "counts" some field that is never empty in any record--such s the primary key.
Sort your records by this calculation field so that you get a group of records for each possible value. Your X series values are the calculation field. The Y series value is the summary field. Then make sure that your records are correctly sorted and your chart's data source option is for "summarized data".