Most “soutien scolaire” has a going rate of about 15€/h around here (Auvergne), which is pretty low, especially if you have to travel to the homes of the school age students. It seems difficult to get more than that, as parents often have an underrated evaluation of the commercial value of teaching in general (ask any state registered teacher whether they feel valued…)
CCI rates seem to be being dragged downwards as well. Currently, the going rate for working for the local CCI language department seems to have been dragged down to about 11-12€/h for blended learning courses, which is in line with other online teaching platforms. Physical presence teaching gets paid at about 18-20€/h.
Private business schools and universities pay a higher hourly rate (38-46€/h), usually aligned to some national higher education pay grid scale for different types of teaching (cours magistral, travaux dirigés, travaux pratique, tutorat, etc). However, the general trend is downwards, as the online teaching market through larg(er) organisations negotiate and snaffle contracts from each other at cut-throat prices.
With your specialisation in maths and stats, you might be better off financially looking at teaching in unis or business schools.
As an aside, many universities, and quite a few business schools, employ teachers on an ad hoc basis, as “vacataires”. These are contracts that are deemed seasonal, even though, they are not, as they are usually repeated year on year, from September to May, and often even through the summer period (summer schools, tutoring, internships, etc), and many of the employers using such vacataire contracts are exploiting a somewhat dubious “oversight” in employment law to allow them to maintain people in precarious employment over decades, with no possibility for the employee to evolve, or even obtain a pay rise, no paid holiday (or an insufficient payment), no sick pay, no access to staff benefits (meal tickets, union representation), etc. As a vacataire, you can also be dismissed on the spot, with no notice (this has happened to someone I know teaching at a university).
Having sussed that these employers are borderline with the French Employment Code, and some of them having been sued at the employment tribunal and lost, quite a few are now “requiring” these vacataires to become autoentrepreneurs, or employees of an umbrella organisation such as a SCOP (who then becomes their principal employer), with a non-negotiable billable hourly rate that shifts all of the financial burden onto the teacher.
As an employer in the private sector, subject to stringent employment laws, I find the whole outsourced language teaching organisation of universities and affiliated business schools quite shocking. Their practices would be severely frowned upon in any normally run business subject to private law, and have employment lawyers banging their heads against the wall in dread, or rubbing their hands in glee, depending on which side they represented. The only reason there are not more cases brought before the employment tribunal is because these employers hold sway over the precarity of employment that they wield with regard to their “employees”. If you sue such an employer, then you might as well be prepared to not find similar work in that region again (and that is a threat they will level at you, should you dare stick your head above the parapet.)
Apologies for the slightly veering off-topic rant, but I felt it important to point out the wider, and oft ignored picture, of teaching as a non-state registered teacher in France.