This article presents an investigation on the educational value of virtual worlds intended for the acquisition of procedural knowledge. This investigation takes as a case of study a virtual laboratory on biotechnology. A remarkable feature in this virtual laboratory is an automatic tutor that supervises student's actions and provides tutoring feedback when it is appropriate. The study presented in this article covers two different aspects of the system. First, it analyzes the impact of this virtual world in learning some concepts related to a biotechnology practice; and second, it surveys the students' opinion on the virtual world by means of three open questions (positive, negative, and general impressions). Results demonstrated that the virtual world had a positive influence in the students' knowledge, and it was well received by them.