Standards improve education in several ways. Standards focus attention on what students are expected to learn from the subject, and standards both specify and address those things that are judged (by the panel of educators and experts who help establish the standards) to be the most critical for students to know about the subject. Standards change a class from a focus on the performance of the students, in comparison to how well the other students are doing, and focus attention instead upon what content each individual student is mastering (learning) about the curriculum. This is similar to the difference between criterion referenced tests which check to see what subject matter the student knows, and the other sort (norm referenced), which compares how well a student did in comparison to all the other students who took the test. Standards are the "criterion reference," and specify the content that students should learn, and also specify what curriculum content teachers should present in their lessons.
In addition, standards improve education across classrooms, schools and states. Standards, especially standards from the national level, ...
Background information on the impact of curriculum standards on modern education, both pros and cons.