Cognitive Tutor has been shown to raise students' math test scores in high school and middle-school classrooms, and their Algebra course was designated one of five exemplary curricula for K-12 mathematics educated by the US Department of Education. There were several research projects conducted by the PACT Center to utilize Cognitive tutor for courses in Excel and to develop an intelligent tutoring system for algebra expression writing, called Ms. Lindquist. Further, in 2005, Carnegie Learning released Bridge to Algebra, a product intended for middle schools that was piloted in over 100 schools. Cognitive tutoring software is continuing to be used. According to a Business Insider Report article, Ken Koedinger, a professor of human-computer interaction and psychology at Carnegie Mellon University, describes how teachers can integrate cognitive tutoring software into the classroom. He suggests that teachers use it in a computer lab environment or during classes. Cognitive tutors can understand the many ways that a student might answer a problem, and then assist the student at the exact time that the help is required. Further, the cognitive tutor can customize exercises specific to the student's needs. Limitations At this time it is unclear whether Cognitive Tutor® is effective at improving student performance. Cognitive Tutor® has had some commercial success however, there may be limitations inherently linked to its design and the nature of intelligent tutoring systems. The following section discusses limitations of Cognitive Tutor® which may also apply to other intelligent tutoring systems. Curriculum At this time, creating a Cognitive Tutor® for all subject areas is not practical or economical. Cognitive Tutor® has been used successfully but is still limited to tutoring algebra, computer programming and geometry because these subject areas have an optimal balance of production rules, complexity and maximum benefit to the learner. The focus of Cognitive Tutor® development has been the design of the software to teach specific production rules and not on the development of curricular content. Despite many years of trials, improvements, and a potential to advance learning objectives, the creators continue to rely primarily on outside sources for curricular direction. Design The complexity of Cognitive Tutor® software requires designers to spend hundreds of hours per instructional hour to create the program. Despite the time invested, the challenges associated with meeting the needs of the learner within the constraints of the design often result in compromises in flexibility and cognitive fidelity. Practicality dictates that designers must