Well, I would suggest to first check and allocate the work with time estimation. If the time is already estimated for the particular task employees are forced to finish the task in given hours and list the employees who are capable enough and finishing the task on time and send notice to the other employees that the strict action will be taken in case they do not improved. Also, consider it as a point while appraisals.
Not at once, but slowly you will see the change.
Not at once, but slowly you will see the change.