Opponents of project-based learning caution against negative outcomes primarily in projects that become unfocused, as underdeveloped assignments or lessons may result in the waste of class time and inability to achieve the learning objectives. Since PBL revolves around student autonomy, student's self-motivation and ability to balance work- time both inside and outside of school are also imperative to a successful project.Deadlinesand areteachers amay realisticbe component of many academic environments, resulting in the implementation of PBLchallenged to often present challenges to teachers in providing students with an ample amount ofsufficient time, flexibility, and resources to be successful.<ref>{{Cite journal |last=Ramos-Ramos |first=Pablo |last2=Botella Nicolás |first2=Ana María |date=2022-08-31 |title=Teaching Dilemmas and Student Motivation in Project-based Learning in Secondary Education |url=http://dx.doi.org/10.14434/ijpbl.v16i1.33056 |journal=Interdisciplinary Journal of Problem-Based Learning |volume=16 |issue=1 |doi=10.14434/ijpbl.v16i1.33056 |issn=1541-5015}}</ref> Furthermore, "Keeping these complex projects on track while attending to students' individual learning needs...requires artful teaching, as well as industrial-strength project management."<ref>{{cite web |title=Projects and Partnerships Build a Stronger Future - Edutopia |url=http://www.edutopia.org/blog/projects-partnerships-pbl-suzie-boss |website=edutopia.org}}</ref>
Opponents of project-based learning caution against negative outcomes primarily in projects that become unfocused, as underdeveloped assignments or lessons may result in the waste of class time. While no one teaching method has been proven more effective than another, critics argue that narratives and presentation of anecdotal evidence included in lecture-style instruction can convey the same knowledge in less class time. Given that disadvantaged students generally have fewer opportunities to learn academic content outside of school, wasted class time due to an unfocused lesson or project presents a particular problem. If the project does not remain on task and content-driven, the project may be ineffective in reaching the learning objectives. Thus, a source of difficulty for teachers includes, "Keeping these complex projects on track while attending to students' individual learning needs...[this] requires artful teaching, as well as industrial-strength project management."<ref>{{cite web |title=Projects and Partnerships Build a Stronger Future - Edutopia |url=http://www.edutopia.org/blog/projects-partnerships-pbl-suzie-boss |website=edutopia.org}}</ref> Thus, like other pedagogical approaches, PBL is only beneficial when applied methodically and effectively.
A specific concern is that PBL may be inappropriate in mathematics, the reason being that mathematics is primarily skill-based at the elementary level. Transforming the curriculum into an over-reaching project or series of projects does not allow for necessary practice of particular mathematical skills. For instance, factoring quadratic expressions in elementary algebra requires extensive repetition {{citation needed|reason=While traditionally taught with extensive rote repetition, more recent & research-driven mathematics pedagogical practices vary on this (ex. in Montessori approaches) |date=March 2019}}.
Another criticism of PBL is that measures that are stated as reasons for its success are not measurable using standard measurement tools, and rely on subjective rubrics for assessing results.{{Citation needed|reason=Research on the fundamental informativeness of quantifiable assessment methods has demonstrated their inaccuracy & inefficacy for educational practice for approx. the last 80 years (see Alfie Kohn's "The Case Against Grades" for an overview of such research). Maybe just needs contextualization for this concern's basis, not citations?|date=March 2019}}
