This is covered by unit tests - but to make sure the web-client is working too: Use this client: https://github.com/moodlehq/sample-ws-clients/blob/master/PHP-REST/client.php /// FUNCTIONNAME core_cohort_create_cohorts /// PARAMETERS $cohort1 = array( 'categorytype' => array('type' => 'system', 'value' => ''), 'name' => 'cohort test 1', 'idnumber' => 'cohorttest1', 'description' => 'This is a description for cohorttest1' ); $params = array('cohorts' => array($cohort1));