The best measure of a student's success at decoding is his oral reading fluency.  To assess a student's oral reading fluency is quite simple.  The teacher has the student read a short,  leveled passage out loud.  The teacher times the student for a minute and counts how many words she reads correctly. It's helpful to count errors as well. For a very reliable reading, it is a good to do 3 separate one-minute timings on different passages and select the middle score.  The QuickReads materials are excellent for these timed readings.  Norms are available to compare the child's performance with a national sample of students in the same grade.

According to these norms, at the end of the school year the median oral reading score

for First graders is about 50 words correctly per minute,

for Second graders is about 90 words correctly per minute and

and for Third graders is about 105 words correct per minute.