A subtest score is an individual score earned on a specific section of a standardized achievement test, such as reading vocabulary, math computation, or spelling, that measures performance in a particular skill area before being combined into composite scores.
What is a Subtest Score?
A subtest score is the individual result from a specific section or component of a standardized achievement test. Comprehensive tests like the Iowa Assessments, Stanford Achievement Test, or California Achievement Test are composed of multiple mini-tests (subtests), each designed to measure a particular skill area. For example, a reading assessment might include separate subtests for vocabulary and reading comprehension, each producing its own score. These individual subtest scores can then be combined to create composite scores that represent broader academic categories. Understanding subtest scores gives parents far more insight into their child's specific strengths and weaknesses than composite scores alone.
Key Takeaways
- Individual scores for specific skill areas within a larger standardized test
- Common subtests include vocabulary, reading comprehension, math computation, and spelling
- Composite scores combine multiple subtests and can mask variations in performance
- Most useful for identifying specific strengths, weaknesses, and curriculum adjustments
- Typically reported as percentile ranks, stanines, grade equivalents, or scaled scores
Common Subtests on Homeschool Standardized Tests
How to Interpret Subtest Scores
Subtest scores are typically reported using several metrics. Percentile rank indicates the percentage of students in the norm group who scored lower. A 72nd percentile in math computation means your child scored higher than 72% of same-grade peers. Stanines use a 1-9 scale where 4-6 is average, 7-9 above average, and 1-3 below average. Many states use the 4th stanine (approximately 23rd percentile) as a minimum threshold. Grade equivalents (like 5.7) are often misinterpreted. A 4th grader scoring 7.2 does not read at 7th-grade level. It means they perform 4th-grade reading tasks as well as an average 7th grader would perform those same 4th-grade tasks.
Why Subtest Scores Matter for Homeschoolers
Composite scores can mask significant variations in performance. A child might score at the 95th percentile in math problem-solving but 45th percentile in computation, producing an average-looking math composite that hides both the strength and the weakness. Examining individual subtest scores reveals where your child excels and where targeted instruction is needed. This precision helps you adjust curriculum effectively. Rather than changing your entire math program, you might add fact fluency practice while accelerating conceptual work. Year-over-year subtest comparisons also track growth patterns better than composite scores, helping you evaluate whether your curriculum choices are working.
State Requirements and Subtest Scores
State requirements vary significantly. Some states like North Carolina require specific subtests in reading, grammar, spelling, and mathematics. Virginia requires a composite score at or above the 4th stanine, combining only math and language arts. Individual subtest scores below threshold are acceptable as long as the composite meets requirements. States like Oregon set minimums around the 15th percentile for composite scores. Eleven states require assessment but have no minimum score requirement, and eleven more have no testing requirement at all. Always check your state's specific requirements to understand which scores matter for compliance.
The Bottom Line
Subtest scores provide the detailed view of academic performance that composite scores obscure. While state compliance may only require overall composite scores, examining individual subtests gives you actionable information for curriculum planning. A strong vocabulary subtest paired with weak reading comprehension points to specific instructional needs that a general "reading" score would miss. Use subtest results to identify patterns: consistent struggles with processing speed, exceptional verbal reasoning, or gaps in specific skill areas that warrant attention. The same test administered yearly allows you to track whether your instruction is producing growth in targeted areas.
