T.S.
It is considered a 3!
Read you schools description of grades to find out what the numbers mean. They are meant to communicate the extent to which a student has demonstrated mastery of the performance standards at their grade level.
If the scale is out of 4, I would think that a 3 means your child is meeting the standard and performing AT grade level. Typically the highest number means ABOVE grade level. The second means the MEET the grade level standard. The next means they haven't met the standard yet, but they are working TOWARD it, and the last means they are BELOW grade level. It isn't a percent correct 90, 80, 70, 60 like the letter grades you're talking about.
Grading scales don't map onto each other the way you're describing. Parents often try to do that, and it does nothing but stress parents, and kids out for NO REASON.
Hope this helps,
T.