As assessment centres are so costly, they are typically the final or penultimate stage of a job application, so you shouldn't fret too much about getting invited to one; it means you've already done pretty well! (allaboutcareers.com)
An assessment centre is usually the final or penultimate stage used in the recruitment process and often involves the simultaneous assessment of a pool of candidates. (matchtech.com)
Often the final or penultimate stage used in the recruitment process, an assessment centre involves the simultaneous assessment of a pool of candidates. (networkerstechnology.com)