When someone does a poor job, treat it as a collective failure.
Don't name names.
Extract lessons learnt as a group.
Always enter the discussion with the assumption that you yourself may have had something to do with the failure. Don't automatically assume it's the other person.
Try to extract why the system allowed this failure to happen. If the failure happened because someone violated our core values, the system or the implied social contract, then speak to this person in private and explain to them how you feel. Give them the chance to fix things.
Don't immediately bring the subject to your Clan/School leader, take the opportunity to resolve things privately first, it will be better for team growth and mutual trust in the long run.
If you are frustrated and feel the need to talk to someone, talk with a trusted neutral party, not a superior, e.g. the Company Therapist is a good choice. The Company Therapist may hold another role in the company, so make sure that it's clear that this is a therapy session and you don't want them acting on the information that you reveal. The Company Therapist is there to provide a listening ear and give some context.
Always attempt to resolve a problem directly with the person in question, privately. This almost always works out better than going to your leader. Only go to your leader if you have tried to resolve the problem privately at least twice with no success.
Focus on one goal, rather than just airing your needs.
Identify the issue from each partner's perspective.
Ask for a time out, if you want one.
Acknowledge that growth together is a process, and allow time for changes to happen.
If the issue can’t be solved right away, then agree to check in from time to time to discuss the issue.
Use I-statements, such as "I felt so angry when x happened.", rather than You-statements, such as "You made me so angry when you did x."
If talking feels difficult, then consider using writing. For example, you can write an email to ask questions, suggest improvements, or describe emotions.
If communication feels blocked, then consider using a third party. For example, consider asking for help from a mediator, or trusted friend.
Only after multiple failed attempts at a private resolution should you notify your leader. When you do this, be decent and inform the other person that you are unhappy with the situation and will inform your leader in an effort to mediate and resolve the situation.