The Lead Developer Model is a venerable and respected way to organise work inside a development team.
It is heavily used in organisations like Microsoft.
In this model, work packages are allocated to a lead developer, who is then responsible for fullfilment of the work. The lead developer will allocate work to the other team members, and coach them through their completion of the work allocated to them.
[Benefit: This model creates healthy incentives for transferring skills, while ensuring tasks are managed by a more senior developer.]
All work should be peer-reviewed at least every 2 days - this keeps the reviewer fresh on what the work item/package is about. Note that this includes the lead developer getting their work reviewed by the others, which is a great knowledge transfer opportunity.
[Benefit: in case of emergency, the reviewer should have enough knowledge to ensure work doesn't get lost]
Where there is no clear "seniority", developers may choose which of them will be the "lead" for a particular project phase.
The normal case is that each lead developer has one or two other developers working with them - it is unusual to put more developers into one group, since that starts to reduce the work efficiency of the lead developer (turning them into a manager). With 4 developers, for example, the ideal structure would be to have two leads, each with one other developer.
Both lead developers and junior developers usually report increased job satisfaction fromt his model: leads because of recognition and the chance to delegate some of the work, and juniors because they get more guidance about what is expected from them, and the chance to understudy a more senior developer.