Background: Online crowdsourcing platforms, such as Amazon Mechanical Turk (MTurk), have become popular alternatives to the ubiquitous student samples used in psychology research. r/SampleSize, an alternative pool on the website Reddit, allows for online participant recruitment without compulsory or immediate payment, making it potentially useful for students, research trainees, and course instructors. Objective: The current study sought to assess the viability of using r/SampleSize as a participant pool by comparing its data characteristics to MTurk and existing lab samples. Method: Two hundred and fifty-six MTurk workers and 277 r/SampleSize participants completed identical questionnaires on demographics, participation motivations, and standard psychology scales. Results: Participants recruited through r/SampleSize reported diverse ages, education levels, income, and employment, although White ethnic background and US residence were predominant. r/SampleSize participants were more internally motivated than MTurk to participate in research and had greater need for cognition but did not differ significantly in altruism or motivation to gain self-knowledge. r/SampleSize data reliability and quality were comparable to MTurk and lab samples across most analyses. Teaching Implications: r/SampleSize can be used to recruit relatively large and diverse samples for undergraduate research projects with minimal setup, labor, and cost. Conclusion: The findings suggest that r/SampleSize is a diverse and viable participant pool.