National assessments of mathematics are often used as an objective measurement of students' knowledge. However, various factors are believed to influence students' achievements on the national assessments, among which students' invested effort. Moreover, students' effort may vary between genders and might be influenced by the presence of external motivational factors, such as grades, or test difficulty. In Italy, no systematic research has studied students' perceived effort on the national assessment of the mathematical knowledge, in particular the relation between the invested effort, the test difficulty and the impact of the external motivational factors, such as grading the national assessment. With the present research, we aimed to investigate students' invested effort in the Italian national assessment of mathematics and its relation to the perceived test difficulty, gender and external motivational factors. Through an online questionnaire with 232 participants, we found that 25.4% of the students put little to no effort. Moreover, when asked about how much more effort would students put if the national assessment was graded, 78.5% of the participants stated they would put more effort than they actually did. The majority of the participants (69.8%) argued that they did not want their standardized test to be graded; however, students who put a greater amount of effort in taking the national assessment would like it to influence their final grade. Lastly, we investigated students' feelings about the test difficulty, finding a negative correlation between students' perception of the difficulty of the test and their invested effort: harder tests are solved with lower effort. Overall, this research suggests that we should carefully interpret the results of the Italian national assessment of mathematics and that policymakers should develop.