The high school admission score that is generally lower is the ACT. The SAT (Scholastic Assessment Test) and ACT (American College Testing) are two of the most widely recognized standardized tests used for college admissions in the United States. On average, the ACT scores are lower than the SAT scores. According to the College Board, the average SAT score for the class of 2021 was 1050 (530 reading, 520 math), while the average ACT composite score was 20.7 (English: 20.8, Math: 20.6, Reading: 21.1, Science: 20.9). This difference can be attributed to the scoring scales and the types of questions on each test.

The SAT has a scoring range of 400-1600, with each section (Reading, Writing and Language, and Math) scored out of 800. The ACT, on the other hand, has a scoring range of 1-36 for each section, with a composite score calculated by averaging the four section scores. The ACT's scoring system is more straightforward, as it does not have the 800-point maximum for each section like the SAT. Additionally, the ACT includes a Science section, which is not present in the SAT, and some students may find the ACT's Science section more challenging.

Another factor contributing to the lower average ACT scores is the demographic makeup of the test-takers. The SAT has a broader demographic representation, including a higher percentage of students from lower-income families, while the ACT is more popular among students from higher-income families and those who attend private schools. These students tend to perform better on standardized tests, which can skew the average scores.

Furthermore, the ACT has a more rigorous scoring process for the Writing section. The SAT Writing and Language section is scored by computer, which can sometimes lead to inconsistencies in scoring. In contrast, the ACT Writing section is scored by human readers, which can result in a more accurate assessment of a student's writing skills.

In conclusion, the ACT is generally the high school admission score that is lower, due to its scoring scale, the inclusion of a Science section, the demographic makeup of test-takers, and the more rigorous scoring process for the Writing section.