Leigh Ann and I have found that planning an inquiry with students is a must, it's a lot of fun too! We are still learning how to make student's voices the loudest but we've found this idea a great step in the direction we are aiming for.
We use Kath Murdoch's Inquiry Cycle (found HERE) on the IWB, or you could do this with marker on large poster paper, to plan a basic overview of our inquiry ahead. It's a great visual and way to manage time with a longer inquiry unit. We return to it during our inquiry to check our time progress and make adjustments to our plan as needed.
In addition we also ask students to plan their inquiry in more detail using an adapted sequence blackline master. They title each box with an inquiry step and then identify, select and write the skills they need to achieve that phase/part/step of the inquiry. This acts as a fantastic formative self assessment for each child to reflect on their progress before moving on to the next stage of their inquiry. Many of our students have learned to become more focused and now understand specific skills help them achieve certain goals. For example; they often find that when Sorting Out the Analysis Thinking Skill is the most useful and often use tools such as Venn Diagrams.