As a second grade teacher, I sometimes have students who can read very well and have a solid grasp of math computation. What they don't have is the ability to explain their work or the higher level thinking skills they need for computation. They are unable to write answers based on inference, analogies, or evaluation.
There are children, however, who will benefit from skipping a year because of the individual circumstances. Meet with the principal and discuss all the advantages and drawbacks and then ask what she would do if it were her child.