Jesus is quoted as speaking of those who are "least in the Kingdom" in two situations: the Sermon on the Mount (or the Plain as in Luke) and in reference to John the Baptist, after John asks if Jesus is "he who is to come."
Matthew 5:19 -- Whoever then relaxes one of the least of these commandments and teaches men so, shall be called least in the kingdom of heaven; but he who does them and teaches them shall be called great in the kingdom of heaven.
Matthew 11:11 (cf. Lk. 7:28) -- Truly, I say to you, among those born of women there has risen no one greater than John the Baptist; yet he who is least in the kingdom of heaven is greater than he.
The first use of "least in the kingdom" seems clear. It refers to someone who relaxes the commandments. The context is that Jesus has urged his followers not only to follow the basic commandments (against murder, adultery, false swearing, etc.) but to go beyond them by not harboring hatred, lust, untruthfulness etc. in one's heart. But the second use raises the question as to whether Jesus believed that John had acted in a similar way to those Jesus spoke of earlier. In other words, did John teach people to relax the basic commandments that Jesus himself endorsed and expanded? And if so, which ones? If not, what did he do to deserve this designation? Or perhaps the two uses of the term simply don't mean the same thing. If so, why would Matthew use the same terminology in 11:11 that he did in 5:19?