The following passage, from Chapter 8:

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"Poor dear fellow!" continued Mrs. Musgrove; "he was grown so steady, and such an excellent correspondent, while he was under your care! Ah! it would have been a happy thing, if he had never left you. I assure you, Captain Wentworth, we are very sorry he ever left you."

It always seems to me that in the matter of reading and writing (and composing of good letters!), "Poor Dick's" education was under the personal care of Wentworth himself. I guess there's no real way of knowing whether he just took special pains because Richard was so awful to begin with, or whether he took it upon himself to ensure all the boys paid due attention to their families at home.