Given the standard scores, it appears that they gave the 6th grade ITBS but had the scores reported as compared to 4th graders. The standard scores for a 6th grader at those percentiles would be more like 280.
Good point. I don't know if the OP's school is testing using the older ITBS or the newer Iowa Assessments, but if it's the present day Iowa test, I had this chart on hand (for grade-level tests). It indicates the 235 falls at the start of 'proficient' for 5th grade for mid-year (75th percentile), and the 242 is the top of proficient for 5th grade spring testing.
Standard Scores Achievement levels for Iowa test Here's a percentile chart (compared to grade-level), which shows you where to compare to 6th graders on that test.
Percentiles and standard scores by grade-level
