Intelligent Tutoring Systems (ITS) are computer systems which provide students with learning environments adapted to their knowledge and learning capabilities. This paper presents SQL-Tutor, an ITS for SQL programming. SQL, the dominant database language, is a simple and highly structured language; yet, students have many difficulties learning it. SQL-Tutor is designed as a guided discovery learning environment which helps students in overcoming these difficulties. We present design issues and the current state in the implementation of the system, with special focus on individualization of instruction towards a particular student.