You must begin attendance and maintain enrollment in your classes to receive your Pell Grant award money. Because Pell Grant funds are disbursed during the semester/quarter, your school's Office of Financial Aid (or its equivalent) will request your enrollment status from the Registrar and, if necessary, recalculate how much you are eligible to receive (based on how often you attend class) before issuing your Pell Grant award. Attendance is crucial; you must show up for your classes regularly.
In order to receive your awarded Pell Grant funding, you must meet your school's "satisfactory academic progress policy," according to The Pell Grant web site (thepellgrant.com). The details of each school's policy vary, so become familiar with your specific requirements to ensure you do not fall below them. Most require a C average or its equivalent for all courses.
The number of times you drop or fail courses (then retake them in order to earn the necessary credits) is also restricted, meaning that, for example, you cannot attempt to earn more than 90 credits in order to earn 60. In short, you only get so many chances to earn the required credits for your certificate, diploma or degree.
If you officially or unofficially withdraw from a course before receiving funds, that course will not be considered when determining the calculation of your Pell Grant award amount. You may have to return funds you received from the Pell Grant if you withdraw from a class after receiving them. By not doing so you risk losing future Pell Grant eligibility. Also, if you drop all of your classes (not just one) before receiving Pell Grant funds, you may still receive some Pell Grant money based on how long you attended the classes (assuming you do not retroactively withdraw from your classes, which eliminates all records of your ever having attended them) before withdrawing from them all. This is called post-withdrawal disbursement.
If you earn a final grade in a course that was not included when your Pell Grant award amount was initially determined, you can ask that your award amount be refigured with that class as a part of the equation.