Gamification refers to the use of game-design elements or mechanisms in non-game contexts to promote the expected behaviours. Though theoretically promising, empirical studies reported mixed results as to the effectiveness of gamification in educational practices. To understand this issue better, this author selected 44 articles on the topic of educational gamification with the use of a bibliometric analysis software "HistCite," followed by a descriptive content analysis on these articles. This author examined three issues, including how effective the educational gamification implementations were in previous empirical studies, how the effectiveness has been measured, and what factors contribute to varied effectiveness results. One significant output of the current study is the redefinition of two terms: game elements refer to "the obvious game-like elements that are frequently used in digital games or gamification, which are concrete nouns", and gamification mechanisms refer to "the underlying guidelines that make gamification activities engaging, which are abstract nouns that relate to humans' innate psychological needs". What's more, the content analysis helped summarise a framework describing what makes gamification engaging, which contains goal, visualisation, immediate feedback, adaptation, challenge, competition, reward, and fun failure. Limitations and suggestions for future studies have been discussed.