There will be the main guide as well as assistant guides who accompany the slowest person in the group. Take note that trekking in high altitude is not about speed and pace. Every day you will have your target destination and whether you reach there in the early afternoon or a few hours late does not really matter. What really is important is that the slower you go, the better you will be able to acclimatize. The Everest Base Camp Trek is not about being the fastest person at all. It is about taking your time, going super slow and having an amazing journey. It is said, the best adventures are not the ones that are rushed or the ones that you just pass by, they are the ones where you stop, look around and take it all step by step.